Polyisocyanates containing uretdione groups

ABSTRACT

A polyisocyanate composition, comprising: A) from 55 to 87% by weight of a polyisocyanate which contains uretdione groups; B) from 10 to 30% by weight of blocking agent, C) from 3 to 30% by weight of polyol having more than two hydroxyl groups and/or chain extender having more than two hydroxyl groups, wherein the polyisocyanate contains more than two terminal, partially or fully blocked isocyanate groups and has a molecular weight of from 1000 to 10,000.

This application is a Continuation of application Ser. No. 08/600,030,filed on Feb. 12, 1996, now U.S. Pat. No. 5,750,727.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to polyisocyanates containing uretdionegroups and having more than two terminal, partially or fully blockedisocyanate groups, to processes for their preparation and to their usein polyurethane coating systems.

2. Discussion of the Background

Polyisocyanates, which especially are used in polyurethane powdercoatings, which contain uretdione groups, are known as described, inparticular, in DE-A 30 30 554. Such polyisocyanates, however, have onlytwo terminal, partially or fully blocked isocyanate groups and arestrictly linear in structure. As disclosed in EP-A-254 154 (page 2,column 1, line 63 to end of sentence), this fact is of greatdisadvantage in practice. A need, therefore, continues to exist for apolyurethane which contains uretdione groups, which exhibits improvedproperties for use in powder coatings.

SUMMARY OF THE INVENTION

Accordingly, one object of the present invention is to providepolyisocyanates which contain uretdione groups which do not have thedisadvantage in structure and the resulting consequences, of the knownuretdione group-containing polyisocyanates.

Briefly, this object and other objects of the present invention ashereinafter will become more readily apparent can be attained byformulations based on polyisocyanates which contain uretdione groups andcomprise

A) from 55 to 87% by weight of polyisocyanate containing uretdionegroups,

B) from 10 to 30% by weight of blocking agent, and

C) from 3 to 30% by weight of polyol having more than two hydroxylgroups and/or chain extender having more than two hydroxyl groups, thepolyisocyanates containing more than two terminal, partially or fullyblocked isocyanate groups and having molecular weights of from 1000 to10,000.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a process for the preparation ofpolyisocyanates containing uretdione groups, in which

1. the NCO groups of the polyisocyanate uretdione (component A) arereacted partially with the calculated quantity of blocking agent(component B), and

2. subsequently, in a second stage, the remaining NCO groups are reactedpartially or completely with (component C).

The invention achieves the production of transparent or pigmentedpolyurethane coating systems, especially powder coatings, of highreactivity, and also provides transparent or pigmented polyurethanepowder coating systems based on polyisocyanates containing uretdionegroups, in combination with hydroxyl-containing polymers.

The uretdiones (component A) employed in the invention are obtained fromdiisocyanates by known methods, and in principle all known diisocyanatescan be employed. Preferred uretdiones, however, originate fromdiisocyanates selected from the group consisting of hexamethylenediisocyanate (HDI), 2-methylpentane-1,5-diisocyanate (DI51),2,2,4(2,4,4)-trimethylhexamethylene diisocyanate and isophoronediisocyanate (IPDI), which can be employed individually or in mixturesas component A. It is particularly preferred to use the uretdione ofisophorone diisocyanate.

The isocyanurate-free uretdione of isophorone diisocyanate is highlyviscous at room temperature, having a viscosity of more than 10⁶ mpa.s;at 60° C. the viscosity is 13×10³ mPa.s and at 80° C. it is 1.4×10³mPa.s. The free NCO content is between 16.8 and 18.5% by weight, i.e.,more or less high amounts of the polyuretdione of IPDI must be presentin the reaction product. The monomer content is ≈1%. The total NCOcontent of the reaction product after heating at 180-200° C. is37.5-37.8% by weight.

Suitable blocking agents (component B) include phenols, alcohols,acetoacetates, lactams, oximes, sterically hindered secondary amines andimidazolines. Particularly preferred blocking agents include caprolactam(CL), acetone oxime, methyl ethyl ketoxime (MEK-ox), cyclohexanoneoxime, methyl isobutyl ketoxime, dicyclohexylamine (DCA) andphenylimidazoline.

Suitable polyols, as component C, include glycerol, trimethylolpropane(TMP), ditrimethylolpropane, trimethylolethane, 1,2,6-hexanetriol,1,2,4-butanetriol, trishydroxyethyl isocyanurate (THEIC),pentaerythritol, mannitol or sorbitol, with trimethylolethane,trimethylolpropane and trishydroxyethyl isocyanurate. They are usedindividually or in mixtures.

The uretdione group-containing polyisocyanates contain, as a chainextender (component C) hydroxy-containing polyesters having a molecularweight of between 250 and 2,000, preferably from 300 to 1,500. They areprepared, for example, by reaction of polyols and dicarboxylic acids.

To prepare the chain extenders, the following polyols are preferablyemployed: glycerol, trimethylolpropane (TMP), ditrimethylolpropane,trimethylolethane, 1,2,6-hexanetriol, 1,2,4-butanetriol,trishydroxyethyl isocyanurate (THEIC), pentaerythritol, mannitol orsorbitol, as well as diethylene glycol, triethylene glycol,tetraethylene glycol, dipropylene glycol, polypropylene glycols,polybutylene glycols, xylylene glycol and neopentylglycolhydroxypivalate. Trimethylolethane, trimethylolpropane andtrishydroxyethyl isocyanurate are preferably employed. They are usedindividually or in mixtures.

The preferred dicarboxylic acids for preparation of the chain extenderinclude aliphatic acids with or without alkyl branching, such assuccinic, adipic, suberic, azelaic and sebacic acid and2,2,4(2,4,4)-trimethyladipic acid. Furthermore, lactones orhydroxycarboxylic acids can also be employed, with particular preferencebeing given to ε-caprolactone and hydroxycaproic acid.

The polyols and chain extenders of component C can in each case beemployed individually or in mixtures, with the mixing ratio beingunimportant.

The polyisocyanates according to the invention, containing uretdionegroups, can be prepared by the following process.

The synthesis occurs in two successive stages, wherein the features ofthe two stages are:

1. The NCO groups of the uretdione (component A) are reacted partiallywith the calculated quantity of blocking agent (component B).

2. Subsequently, in the second stage, the remaining NCO groups arereacted partially or completely with component C.

The reactions in both stage 1 and stage 2 can each be performed with orwithout solvent. If used, the solvent can be selected from the groupconsisting of aromatic and aliphatic hydrocarbons such as benzene,toluene, ethyl acetate, butyl acetate, acetone, methyl ethyl ketone,methyl isobutyl ketone and chlorinated aromatic and aliphatichydrocarbons, as well as any desired mixtures of these or other inertsolvents.

If the reaction is carried out without solvent, the reaction of stage 1is performed batchwise or, preferably, continuously using a "staticmixer". The reaction of stage 2 takes place in an intensive kneadingapparatus, preferably using a twinscrew extruder. In addition, catalystscan be used to accelerate the reaction and if so are employed in aconcentration of from 0.01 to 1% by weight, particularly preferably from0.03 to 0.5% by weight. Preference is given to the use, as catalyst, oforganotin compounds. Particular mention is made here of dibutyltindilaurate (DBTL). Other catalysts, however, should not be regarded asbeing unsuitable in principle.

The uretdione group-containing polyisocyanates of the invention can beused in particular in polyurethane powder coating systems, whichsurprisingly exhibit increased reactivity. The polyurethane powdercoating systems of the invention comprise the uretdione group-containingpolyisocyanates of the invention in combination with hydroxyl-containingpolymers.

Suitable co-reactants for PU powder coatings are compounds which carryfunctional groups which, during the curing process, react withisocyanate groups as a function of temperature and time. Examples of thecompounds include those which contain hydroxyl, carboxyl, mercapto,amino, urethane and (thio)urea groups. Polymers which can be employedinclude addition polymers, condensation polymers and polyadditioncompounds.

Preferred co-reactant components are primarily polyethers,polythioethers, polyacetals, polyester amides, epoxy resins havinghydroxyl groups in the molecule, amino resins and their modificationproducts with polyfunctional alcohols, polyazomethines, polyurethanes,polysulfonamides, melamine derivatives, cellulose esters and celluloseethers, partially hydrolysed homo- and copolymers of vinyl esters, butespecially polyesters and acrylic resins.

Preferred carboxylic acids for the preparation of polyesters includealiphatic, cycloaliphatic, aromatic and/or heterocyclic compounds innature and may if desired be substituted by halogen atoms and/or may beunsaturated. Suitable examples of acid compounds include succinic,adipic (As), suberic, azelaic, sebacic, phthalic, terephthalic (Ts),isophthalic (Is), trimellitic, pyromellitic, tetrahydrophthalic,hexahydrophthalic, hexahydroterephthalic, di- and tetrachlorophthalic,endomethylenetetrahydrophthalic, glutaric, maleic and fumaric acids and,when available, their anhydrides, dimethyl terephthalate (DMT),bisglycol terephthalate, and also cyclic monocarboxylic acids such asbenzoic acid, p-tert-butylbenzoic acid and hexahydrobenzoic acid.

Suitable examples of polyhydric alcohols for polyester preparationinclude ethylene glycol, 1,2-propylene glycol and 1,3-propylene glycol,1,4-butylene glycol and 2,3-butylene glycol,di-β-hydroxyethylbutanediol, 1,6-hexanediol, 1,8-octanediol,neopentylglycol, cyclohexanediol, bis(1,4-hydroxymethyl)cyclohexane,2,2-bis(4-hydroxycyclohexyl)propane, 2,2-bis4-(β-hydroxyethoxy)phenyl!propane, 2-methyl-1,3-propanediol,3-methyl-1,5-pentanediol, 2,2,4(2,4,4)-trimethyl-1,6-hexanediol,glycerol, trimethylolpropane, trimethylolethane, 1,2,6-hexanetriol,1,2,4-butanetriol, tris(β-hydroxyethyl) isocyanurate, pentaerythritol,mannitol and sorbitol and also diethylene glycol, triethylene glycol,tetraethylene glycol, dipropylene glycol, polypropylene glycols,polybutylene glycols, xylylene glycol and neopentylglycolhydroxypivalate.

It is also possible to employ mono- and polyesters as lactones such as,for example, ε-caprolactone, and hydroxy-carboxylic acids, for example,hydroxypivalic acid, ψ-hydroxydecanoic acid, ψ-hydroxycaproic acid, andthioglycolic acid. Polyesters of the above-mentioned polycarboxylicacids and/or their derivatives and polyphenols, such as hydroquinone,bisphenol A, 4,4'-dihydroxybiphenyl and bis(4-hydroxyphenyl) sulfone;polyesters of carbonic acid which are obtainable from hydroquinone,diphenylolpropane, p-xylylene glycol, ethylene glycol, butanediol or1,6-hexanediol and other polyols by customary condensation reactions,for example with phosgene or with diethyl or diphenyl carbonate, or fromcyclic carbonates such as glycol carbonate or vinylidene carbonate, bypolymerization in a known manner; polyesters of silicic acid, polyestersof phosphoric acid, for example, of methane-, ethane-, β-chloroethane-,benzene- or styrene-phosphoric acid, -phosphoryl chloride or -phosphoricester and polyalcohols or polyphenols of the above-mentioned type;polyesters of boric acid; polysiloxanes, for example, prepared byhydrolysis of dialkyldichlorosilanes with water and subsequent treatmentwith polyalcohols, and polysiloxanes prepared by addition ofpolysiloxane dihydrides with ethylenically unsaturated compounds such asallyl alcohol or acrylic acid.

Preferred polyesters also include, for example, the reaction products ofpolycarboxylic acids and glycidyl compounds, as described for example inDE-C 24 10 513.

The hydroxyl-containing polyesters which are employed with particularpreference have an OH functionality of >2, an OH number of from 20 to200 mg of KOH/g, preferably from 30 to 150 mg of KOH/g, a viscosity of<60,000 mpa.s, preferably <40,000 mPa.s, at 140° C. and a melting pointof >70° C. to ≦120° C., preferably from 75° C. to 100° C.

Suitable examples of glycidyl compounds which can be used include (1)esters of 2,3-epoxy-1-propanol with monobasic acids having 4 to 18carbon atoms such as glycidyl palmitate, glycidyl laurate and glycidylstearate, (2) alkylene oxides having 4 to 18 carbon atoms such asbutylene oxide, and (3) glycidyl ethers such as octyl glycidyl ether.

Dicarboxylic acids which can be used in this process are all of thepolycarboxylic acids listed below under 2. Monocarboxylic acids whichare listed below under 3, for example, can likewise be employed.

Preferred components also include monomeric esters, for examplebis(hydroxy(alcohol) dicarboxylates, monocarboxylic esters ofmore-than-divalent polyols, and oligoesters which can be prepared bycondensation reactions from the base materials which are customary inpaint chemistry. Examples of compounds which can be regarded as suchare:

1. Alcohols having 2 to 24 carbon atoms, preferably 2 to 10 carbonatoms, and 2 to 6 OH groups attached to nonaromatic carbon atoms, forexample ethylene glycol, propylene glycol, diethylene glycol,dipropylene glycol, butanediols, neopentylglycol, hexanediols,hexanetriols, perhydrobisphenol, dimethylolcyclohexane, glycerol,trimethylolethane, trimethylolpropane, pentaerythritol,dipentaerythritol and mannitol.

2. Di- and polycarboxylic acids having 4 to 36 carbon atoms and 2 to 4carboxyl groups and esterifiable derivatives thereof, such as anhydridesand esters, for example phthalic acid (phthalic anhydride), isophthalicacid, terephthalic acid, alkyltetrahydrophthalic acid,endomethylenetetrahydrophthalic anhydride, adipic acid, succinic acid,maleic acid, fumaric acid, dimeric fatty acids, trimellitic acid,pyromellitic acid and azelaic acid.

3. Monocarboxylic acids having 6 to 24 carbon atoms, for examplecaprylic acid, 2-ethylhexanoic acid, benzoic acid, p-tert-butylbenzoicacid, hexahydrobenzoic acid, monocarboxylic acid mixtures of naturaloils and fats, such as coconut fatty acid, soya oil fatty acid,ricinenic fatty acid, hydrogenated and isomerized fatty acids, such as"Konjuvandol" fatty acid and mixtures thereof, it also being possiblefor the fatty acids to be employed as glycerides and to be reacted intransesterification and/or dehydration reactions.

4. Monohydric alcohols having 1 to 18 carbon atoms, for examplemethanol, ethanol, isopropanol, cyclohexanol, benzyl alcohol,isodecanol, nonanol, octanol and oleyl alcohol.

The polyesters can be prepared in a manner known per se by condensationin an inert gas atmosphere at temperatures of from 100 to 260° C.,preferably from 130 to 220° C., in the melt or by an azeotropicprocedure, as described for example in Methoden der Organischen ChemieMethods of Organic Chemistry! (Houben-Weyl), vol. 14/2, 1-5, 21-23,40-44, Georg Thieme Verlag, Stuttgart, 1963 or in C.R. Martens, AlkydResins, 51-59, Reinhold Plastics Appl. Series, Reinhold PublishingComp., New York, 1961.

Preferred acrylate resins which can be used as OH components includehomo- or copolymers, in which case, for example, the following monomerscan be selected as starting compounds: (1) esters of acrylic acid andmethacrylic acid with dihydric, saturated, aliphatic alcohols having 2to 4 carbon atoms, for example 2-hydroxyethyl acrylate, 2-hydroxypropylacrylate, 4-hydroxybutyl acrylate and the corresponding methacrylates;(2) acrylic and methacrylic alkyl esters having 1 to 18 carbon atoms inthe alcohol component, such as methyl acrylate, ethyl acrylate, propylacrylate, isopropyl acrylate, n-butyl acrylate, tert-butyl acrylate,2-ethylhexyl acrylate, stearyl acrylate and the correspondingmethacrylates; (3) cyclohexyl acrylate and cyclohexyl methacrylate; (4)acrylonitrile and methacrylonitrile, acrylamide and methacrylamide; and(5) N-methoxymethyl(meth)acrylamide.

Particularly preferred acrylate resins include copolymers of

a. from 0 to 50% by weight of esters of acrylic or methacrylic acid withdihydric or higher polyhydric alcohols such as 1,4-butanediolmonoacrylate, hydroxypropyl (meth)acrylate; and also vinylglycol,vinylthioethanol, allyl alcohol and 1,4-butanediol monovinyl ether;

b. from 5 to 95% by weight of esters of acrylic acid or methacrylic acidwith monohydric alcohols containing 1 to 12 carbon atoms such as methylmethacrylate, ethyl acrylate, n-butyl acrylate and 2-ethylhexylacrylate;

c. from 0 to 50% by weight of aromatic vinyl compounds such as styrene,methylstyrene and vinyltoluene;

d. from 0 to 20% by weight of other monomers containing functionalgroups, for example acrylic acid, methacrylic acid, crotonic acid,itaconic acid, maleic acid, fumaric acid, maleic anhydride, maleicmonoester, acrylamide, methacrylamide, acrylonitrile orN-methylol(meth)acrylamide and glycidyl (meth)-acrylate.

The amount of Group a. and/or Group b. in the acrylate resin is at least5% by weight.

The acrylate resins can be prepared by such customary methods assolution, suspension, emulsion and precipitation polymerization.However, they are preferably prepared by bulk polymerization, which canbe initiated by means of UV light.

Other suitable polymerization initiators include the usual peroxides andazo compounds, such as, for example, dibenzoyl peroxide, tert-butylperbenzoate and azodiisobutyronitrile. The molecular weight of theacrylate resins can be regulated, for example, with sulfur compoundssuch as tert-dodecyl mercaptan.

Preferred polyethers can be prepared, for example, by polyaddition ofepoxides such as ethylene oxide, propylene oxide, butylene oxide,trimethylene oxide, 3,3-bis(chloromethyl)oxacyclobutane,tetrahydrofuran, styrene oxide, the 2,5-bis(epoxypropyl) ether ofdiphenylolpropane or epichlorohydrin with itself, for example in thepresence of BF₃, or by addition reaction of these epoxides, individuallyor mixed or in succession, with starting components containing reactivehydrogen atoms, such as alcohols or amines, examples being water,ethylene glycol, 1,3-propylene glycol or 1,2-propylene glycol,pentamethylene glycol, hexanediol, decamethylene glycol,trimethylolpropane, 4,4'-dihydroxydiphenylpropane, aniline, ammonia,ethanolamine, ethylenediamine, di(β-hydroxypropyl)methylamine,di(β-hydroxyethyl)aniline, hydrazine and also hydroxyalkylated phenols,for example di(β-hydroxyethoxy)resorcinol.

It is likewise possible to employ hydroxyl-containing polyurethanesand/or polyureas.

As hydroxyl-containing polymers, it is of course also possible to employmixtures of two or more substances.

The mixing ratio of the hydroxyl-containing polymers and the uretdionegroup-containing polyisocyanates is generally chosen such that there is0.6-1.2, preferably 0.8-1.1 and, most preferably, 1.0 NCO group per OHgroup.

For the production of PU powder coatings, the isocyanate component ismixed with the appropriate hydroxyl-containing polymer and, if desired,catalysts and also pigments and customary auxiliaries such as fillersand levelling agents, e.g. silicone oil, acrylate resins, and themixture is homogenized in a melt. This can take place in a suitableapparatus, for example, in heatable kneading equipment, but preferablyby extrusion, in which case upper temperature limits of from 130 to 140°C. should not be exceeded. The extruded composition, after cooling toroom temperature and after appropriate comminution, is around to aready-to-spray powder. The application of the ready-to-spray powder tosuitable substrates can be carried out by known methods, for example, byelectrostatic powder spraying, fluidized-bed sintering, or electrostaticfluidized-bed sintering. After application of the powder, the coatedworkpieces are heated for curing purposes for from 60 to 4 minutes at atemperature of from 150 to 220° C., preferably from 30 to 6 minutes atfrom 160 to 200° C.

Having generally described this invention, a further understanding canbe obtained by reference to certain specific examples which are providedherein for purposes of illustration only and are not intended to belimiting unless otherwise specified.

A Preparation of the Uretdione Group-containing Polyisocyanates of theinvention

A 1 Polyol Chain Extenders

General preparation procedure

The starting components, see Table 1, are placed in a reactor and heatedin an oil bath to ≈140° C. After the substances have largely melted,0.1% by weight of di-n-butyltin oxide is added as catalyst. Initialelimination of water takes place at from 150 to 160° C. The temperatureis raised to from 180° C. to 190° C. over the course of from 2 to 3hours and the esterification is brought to completion over a further 8to 10 hours. During the entire reaction period, the bottom product isstirred and a weak stream of nitrogen is passed through the reactionmixture. The acid number of the polyester is always <2 mg of KOH/g.

                  TABLE 1                                                         ______________________________________                                        Polyol chain extender                                                                          Characteristics                                              Example                                                                              Starting components in mol                                                                    OH number  Viscosity at                                A1     As     NPG    HD   TMP  mg KOH/g 25° C. mPa ·          ______________________________________                                                                                s                                     1      2      1      1    1    270-285  5,500                                 2      Polycaprolactones                                                                             535-550      240                                              Interox-Capa 304                                                       3      Polycaprolactones                                                                             305-320    1,350                                              Interox-Capa 305                                                       4      Polycaprolactones                                                                             210-220    2,300                                              Interox-Capa 316                                                       ______________________________________                                    

A 2 Polyisocyanates Containing Uretdione Groups

General preparation procedures

A 2.1 With solvent

The uretdione or a uretdione mixture, see Table 2, and the catalyst(from 0.03 to 1% by weight) are introduced into the reactor as asolution in the solvent. With vigorous stirring and under an inert gasatmosphere, the calculated quantity of blocking agent is added rapidlyin portions at a rate such that the reaction temperature does not exceed100° C. The reaction is monitored by titrimetric NCO determination; thereaction time of the first stage is from 2 to 5 hours. Subsequently, thecalculated quantity of polyol and/or chain extender, see Table 2, isadded to the partially blocked uretdione at a rate such that thereaction temperature does not exceed 100° C. After the end of additionof the OH component, stirring is continued until the NCO content hasfallen to <1% by weight. Subsequently, the solvent is removed and theproduct is cooled and, if desired, comminuted.

A 2.2 Without Solvent

For the solvent-free preparation, the uretdione is likewise reacted inthe first step with the calculated quantity of blocking agent, see Table2. The required quantity of catalyst of from 0.1 to 1% by weight, basedon end product is added during stage 1. After the end of the reaction,the partially blocked uretdione is fed at a temperature of from 80 to150° C., together with the preheated (from 25 to 130° C.) polyol and/orchain extender, into a twin-screw extruder.

The extruder employed is composed of ten barrels, of which five areheating zones. The temperatures of the heating zones are within a widerange, between 50 and 180° C., and can be controlled individually. Alltemperatures are setpoint temperatures, and regulation in the barrelstakes place by electric heating and pneumatic cooling. The die elementis heated by an oil thermostat. The rotary speed of the twin screwfitted with conveying elements was between 50 and 380 rpm.

The reaction product, obtained in a quantity of from 10 to 130 kg/h, iseither cooled, then comminuted or shaped and bagged, or else the melt isshaped, cooled and bagged.

The physical and chemical characteristics of the process products andthe molar compositions are shown in Table 2.

The uretdiones, prepared by known processes, has, the following NCOcharacteristics:

IPDI uretdione

NCO-free: from 16.8 to 18.5% by weight

total NCO: from 37.4 to 37.8% by weight

DI51 uretdione

NCO-free from 20.1 to 21.2% by weight

total NCO: from 43.7 to 44.9% by weight

HDI uretdione (Desmodur® N 3400)

NCO-free: from 20.9 to 22.1% by weight

total NCO: from 35.6 to 36.5% by weight

                                      TABLE 2                                     __________________________________________________________________________    Polyisocyanates containing uretdione groups                                                              Chemical and physical                                                         characteristics                                                                           Glass                                                                         transi-                                Composition in (mol)       NCO content tion                                   Uretdione  Blocking   Chain                                                                              (% by weight)                                                                        Melting                                                                            tempera-                               Example                                                                            of    agent                                                                              Polyol                                                                              extender                                                                           free                                                                              total                                                                            range ° C.                                                                  ture                                   __________________________________________________________________________    1    IPDI (3)                                                                            CL (3)                                                                             THEIC (1)                                                                           --   <0.1                                                                              19.5                                                                             130-132                                                                            77-95                                  2    IPDI (6)                                                                            CL (9)                                                                             THEIC (1)                                                                           --   0.1 22.2                                                                             110-117                                                                            45-67                                  3    IPDI (3)                                                                            CL (3)                                                                             TMP (1)                                                                             --   0.3 20.6                                                                             129-135                                                                             75-100                                4    IPDI (3)                                                                            CL (2.5)                                                                           TMP (1)                                                                             --   0.8 21.9                                                                             131-134                                                                             99-105                                5    IPDI (3)                                                                            CL (2)                                                                             TMP (1)                                                                             --   1.3 21.7                                                                             139-142                                                                            103-125                                6    IPDI (4)                                                                            CL (5)                                                                             TMP (1)                                                                             --   0.4 21.6                                                                             113-116                                                                            63-85                                  7    IPDI (6)                                                                            CL (9)                                                                             TMP (1)                                                                             --   0.1 23.0                                                                             106-108                                                                            49-72                                  8    IPDI (6)                                                                            CL (8)                                                                             TMP (1)                                                                             --   0.6 22.8                                                                             105-109                                                                            51-66                                  9    IPDI (3)                                                                            CL (3)                                                                             --    A1 (1)                                                                             <0.1                                                                              17.0                                                                             86-89                                                                              46-63                                  10   IPDI (2.4)                                                                          CL (2.4)                                                                           --    A2 (1)                                                                             0.2 19.5                                                                             94-97                                                                              48-57                                  11   IPDI (3)                                                                            CL (3)                                                                             --    A3 (1)                                                                             <0.1                                                                              17.6                                                                             87-90                                                                              51-60                                  12   IPDI (4)                                                                            CL (4)                                                                             --    A4 (1)                                                                             0.2 15.8                                                                             74-77                                                                              23-45                                  13   IPDI (3)                                                                            CL (3)                                                                             TMP (0.75)                                                                          A3 (0.25)                                                                          0.1 20.5                                                                             117-120                                                                            77-91                                  14   IPDI (3)                                                                            CL (3)                                                                             TMP (0.5)                                                                           A3 (0.5)                                                                           0.2 19.1                                                                             106-111                                                                            59-70                                  15   IPDI (3.5)                                                                          CL (3.5)                                                                           TMP (0.5)                                                                           A4 (0.5)                                                                           0.5 17.9                                                                             101-104                                                                            60-78                                  16   IPDI (3.5)                                                                          CL (3.5)                                                                           A3 (0.5)                                                                            A4 (0.5)                                                                           0.2 16.5                                                                             93-96                                                                              46-66                                  17   DI51 (3)                                                                            CL (3)                                                                             THEIC (1)                                                                           --   0   22.3                                                                             28-33                                                                              (-2)-                                                                         (+12)                                  18   DI51 (3)                                                                            CL (3)                                                                             TMP (1)                                                                             --   0   23.6                                                                             25-30                                                                              (-4)-                                                                         (+10)                                  19   IPDI (2)                                                                            CL (3)                                                                             TMP (1)                                                                             --   <0.1                                                                              22.2                                                                             96-99                                                                              45-66                                       DI51 (1)                                                                 20   IPDI(1)                                                                             CL (3)                                                                             TMP (1)                                                                             --   <0.1                                                                              22.9                                                                             70-74                                                                              41-58                                       DI51 (2)                                                                 21   IPDI (2)                                                                            CL (3)                                                                             TMP (1)                                                                             --   <0.1                                                                              20.1                                                                              97-100                                                                            62-76                                       N 3400 (1)                                                               22   IPDI (3)                                                                            MEK-ox                                                                             TMP (1)                                                                             --   0.2 22.3                                                                              99-102                                                                            56-72                                             (3)                                                                23   IPDI (3)                                                                            DCA (3)                                                                            TMP (1)                                                                             --   0.1 19.3                                                                             126-128                                                                             97-111                                24   IPDI (3)                                                                            MEK-ox                                                                             TMP (0.5)                                                                           A3 (0.5)                                                                           <0.1                                                                              19.9                                                                             75-81                                                                              42-58                                             (3)                                                                __________________________________________________________________________

B Polyester

Table 3 below gives an overview of the polyesters commercially availablefor the formulation of PU powder coatings.

                                      TABLE 3                                     __________________________________________________________________________                     Chemical and physical characteristics                                                           Glass                                                       OH number         transition                                                                          Viscosity                            Example                                                                            Producer    mg of Acid number                                                                          Melting                                                                            temperature                                                                         at 160° C.                    B    Country                                                                             Designation                                                                         KOH/g mg of KOH/g                                                                          range ° C.                                                                  ° C.                                                                         mPa · s                     __________________________________________________________________________    1    Hoechst AG                                                                          Alftalat                                                                            55-60 2-4    82-90                                                                              >50   24-29,000                                 Italy AN 739                                                             2    DSM   Uralac                                                                              38-41   4-4.5                                                                              70-75                                                                               50   40,000                                    Netherlands                                                                         P 1460                                                             3    UCB   Crylcoat                                                                            26-31 3-4    74-80                                                                              >50   33-38,000                                 Belgium                                                                             240                                                                __________________________________________________________________________

C Polyurethane Powder Coatings

General Preparation Procedure

The comminuted products, uretdione group-containing polyisocyanates(crosslinking agents), polyesters, levelling agent master batch and, ifappropriate, catalyst masterbatch are intimately mixed with or withoutthe white pigment in an edge runner mill and then homogenized in anextruder at a maximum temperature of 130° C. After cooling, theextrudate is fractionated and ground with a pinmill to a particle size<100 μm. The powder thus prepared is applied with an electrostaticpowder spraying unit at 60 kV to degreased, optionally pretreated ironpanels which are baked in a convection oven at temperatures between 160and 200° C.

Levelling Agent Masterbatch

A 10% by weight amount of the levelling agent, which is a commercialcopolymer of butyl acrylate and 2-ethylhexyl acrylate, is homogenized inthe melt in the corresponding polyester and comminuted after havingsolidified.

Catalyst Masterbatch

A 5% by weight of the catalyst--DBTL--is homogenized in the melt in thecorresponding polyester and comminuted after having solidified.

The abbreviations in the tables below have the following meanings:

LT=layer thickness in μm

HK=Konig hardness (sac) (DIN 53 157)

HB=Buchholz hardness (DIN 53 153)

EI=Erichsen indentation (DIN 53 156)

CH=Crosshatch test (DIN 53 151)

GG 60° aspect=Gardner gloss (ASTM-D 5233) measurement

Imp. rev. Impact reverse in g.m

C 1 Transparent Powder Coatings

In accordance with the process described, the transparent powdercoatings were prepared, applied and baked at between 160 and 200° C.

                                      TABLE 4                                     __________________________________________________________________________    Clearcoats                                                                    Example C1                                                                    Formulation 1   2   3   4    5   6   7                                        __________________________________________________________________________    Crosslinking agent                                                                        18.72                                                                             17.9                                                                              12.69                                                                             9.83 17.22                                                                             20.33                                                                             19.04                                    according to A 2                                                              Table 2 (Example)                                                                         (1) (3) (3) (3)  (6) (11)                                                                              (13)                                     Polyester according to B 1                                                                81.28                                                                             82.1                                                                              --  --   82.78                                                                             79.67                                                                             80.96                                    Polyester according to B 2                                                                --  --  87.31                                                                             --   --  --  --                                       Polyester according to B 3                                                                --  --  --  91.17                                                                              --  --  --                                       Notes:      All formulations contained 0.5% by weight each of levelling                   agent                                                                         and benzoin and 0.1% by weight of DBTL; the OH/NCO ratio =                    1:1                                                               Coating data                                                                  LT          63-75                                                                             66-77                                                                             68-81                                                                             63-80                                                                              71-80                                                                             64-81                                                                             71-82                                    HK          207 209 213 199  203 201 198                                      HB          100 100 100 100  100 100 100                                      CH          0   0   0   0    0   0   0                                        EI          >10 >10 >10 >10  >10 >10 >10                                      Notes:      Curing conditions: 200° C./6-8 minutes, 180°                    C./12-15 minutes,                                                             170° C./18-20 minutes                                      __________________________________________________________________________

                                      TABLE 5                                     __________________________________________________________________________    Pigmented Powder Coatings                                                     __________________________________________________________________________    Example C 2                                                                   Formulation                                                                           1   2   3   4   5*) 6   7   8*) 9   10  11  12                        __________________________________________________________________________    Crosslinking                                                                          18.72                                                                             9.62                                                                              16.83                                                                             17.9                                                                              14.85                                                                             12.69                                                                             9.83                                                                              8.02                                                                              17.22                                                                             9.42                                                                              8.97                                                                              20.33                     agent according                                                               to A 2                                                                        Table 2 (1) (1) (2) (3) (3) (3) (3) (3) (6) (6) (8) (11)                      (example)                                                                     Polyester                                                                             81.28                                                                             --  83.17                                                                             82.1                                                                              85.15                                                                             --  --  --  82.78                                                                             --  --  79.67                     according to B 1                                                              Polyester                                                                             --  --  --  --  --  87.31                                                                             --  --  --  --  --  --                        according to B 2                                                              Polyester                                                                             --  90.38                                                                             --  --  --  --  90.17                                                                             91.98                                                                             --  90.58                                                                             91.03                                                                             --                        according to B 3                                                              Notes:  All formulations contain 40% by weight of TiO.sub.2 (white                    pigment) and 0.5% by weight each of levelling agent and                       benzoin, and also 0.15% by weight of DBTL; the OH/NCO ratio -                 1:1;*) 1:0.8                                                          Coating data                                                                  LT      60-80                                                                             58-83                                                                             50-60                                                                             56-73                                                                             52-66                                                                             60-73                                                                             55-66                                                                             50-63                                                                             50-62                                                                             61-70                                                                             57-71                                                                             59-74                     HK      189 189 181 180 183 185 181 172 182 173 175 171                       HB      111 111 125 100 100 100 100 100 100 100 100 100                       CH      0   0   0   0   0   0   0   0   0   0   0   0                         GG 60° aspect                                                                  88  88  87  89-90                                                                             88  89  89-90                                                                             91-92                                                                             90  91-92                                                                             90  90                        SI      >10 >10 >10 >10 >10 >10 >10 >10 >10 >10 >10 >10                       Imp. rev.                                                                             >944.6                                                                            >944.6                                                                            >944.6                                                                            >944.6                                                                            >944.6                                                                            >944.6                                                                            >944.6                                                                            >944.6                                                                            >944.6                                                                            >944.6                                                                            >944.6                                                                            >944.6                    Notes:  Curing conditions: 200° C/8-10 minutes or 180°                  C./15-20 minutes                                                      __________________________________________________________________________    Example C 2                                                                   Formulation                                                                           13  14  15  16  17*)                                                                              18  19*)                                                                              20  21  22  23  24                        __________________________________________________________________________    Crosslinking                                                                          14.54                                                                             17.97                                                                             12.75                                                                             9.87                                                                              89.54                                                                             20.06                                                                             11.80                                                                             16.83                                                                             11.88                                                                             17.97                                                                             16.83                                                                             18.98                     agent according                                                               to A 2                                                                        Table 2 (11)                                                                              (13)                                                                              (13)                                                                              (13)                                                                              (13)                                                                              (15)                                                                              (15)                                                                              (19)                                                                              (19)                                                                              (21)                                                                              (22)                                                                              (23)                      (example)                                                                     Polyester                                                                             --  82.03                                                                             --  --  --  79.94                                                                             --  83.17                                                                             --  82.03                                                                             83.17                                                                             81.12                     according to B 1                                                              Polyester                                                                             85.86                                                                             --  87.25                                                                             --  10.46                                                                             --  88.20                                                                             --  88.12                                                                             --  --  --                        according to B 2                                                              Polyester                                                                             --  --  --  90.13                                                                             --  --  --  --  --  --  --  --                        according to B 3                                                              Notes:  All formulations contain 40% by weight of TiO.sub.2 (white                    pigment) and 0.5% by weight each of levelling agent and                       benzoin, and also 0.15% by weight of DBTL; the OH/NCO ratio -                 1:1;*) 1:0.8                                                          Coating data                                                                  LT      65-71                                                                             57-65                                                                             63-70                                                                             59-75                                                                             64-81                                                                             71-84                                                                             65-78                                                                             64-71                                                                             73-87                                                                             65-83                                                                             50-60                                                                             55-65                     HK      173 181 183 179 177 174 177 175 176 172 171 187                       HB      100 100 100 100 100 100 100 100 100 100 100 111                       CH      0   0   0   0   0   0   0   0   0   0   0   0                         GG 60° aspect                                                                  90  90  89-91                                                                             90-92                                                                             90  91-92                                                                             90  89-90                                                                             90  89-90                                                                             89  87                        EI      >10 >10 >10 >10 >10 >10 >10 >10 >10 >10 >10 >10                       Tmp. rev.                                                                             >944.6                                                                            >944.6                                                                            >944.6                                                                            >944.6                                                                            >944.6                                                                            >944.6                                                                            >944.6                                                                            >944.6                                                                            >944.6                                                                            >944.6                                                                            >944.6                                                                            >944.6                    Notes:  Curing conditions: 200° C./8-10 minutes or 180°                 C./15-20 minutes                                                      __________________________________________________________________________

Having now fully described the invention, it will be apparent to one ofordinary skill in the art that many changes and modifications can bemade thereto without departing from the spirit or scope of the inventionas set forth herein.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:
 1. A composition comprising a blockedpolyisocyante product having a molecular weight of from 1000 to 10,000and obtained by a process comprising: i) partially reacting from 55 to87%, by weight of the product, of a uretdione containing isocyanategroups (component A) with from 10 to 30%, by weight of the product ofblocking agent (component B) to block at least one but less than all theisocyanate groups of the uretdione; and ii) subsequently, reacting allor some of the remaining NCO groups, with from 3 to 30% by weight of theproduct of a polyol having more than two hydroxyl groups or a polyesteror polycaprolactone chain extender having more than two hydroxyl groupscomponent C).
 2. The composition of claim 1, wherein said molecularweight ranges from 1500 to
 5000. 3. The composition of claim 1, whereinsaid uretdione is derived from the diisocyanates: hexamethylenediisocyanate, 2-methylpentane-1,5-diisocyanate,2,2,4(2,4,4)-trimethylhexamethylene diisocyanate and isophoronediisocyanate, which are employed individually or in mixtures.
 4. Thecomposition of claim 1, wherein said blocking agent is a phenol, analcohol, an acetoacetate, a lactam, an oxime, or a sterically hinderedsecondary amine or imidazoline.
 5. The composition of claim 1, whereinsaid blocking agent is caprolactam, acetone oxime, methyl ethylketoxime, cyclohexanone oxime, methyl isobutyl ketoxime,dicyclohexylamine or phenylimidazoline.
 6. The composition of claim 1,wherein said polyol is trimethylolethane, trimethylolpropane,trishydroxyethyl isocyanurate, or mixtures thereof.
 7. The compositionof claim 1, wherein said chain extender is a polyester orpolycaprolactone having a functionality of more than two, a molecularweight of between 230 and 2000 and a hydroxyl number of between 600 and100.
 8. The composition of claim 1, wherein said chain extender is apolyester or a polycaprolactone having a functionality of more than 2, amolecular weight of between 250 and 1000 and a hydroxyl number ofbetween 550 and
 250. 9. The composition of claim 7, wherein said chainextender is derived from at least one mol of polyol selected from thegroup consisting of trimethylolethane, trimethylolpropane,trishydroxyethyl isocyanurate and pentaerythritol.
 10. The compositionof claim 7, wherein said chain extender is derived from ε-caprolactone,hydroxycaproic acid or combinations thereof.